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A more accurate, real-world design informs the updates to SAP calculations.

As we know, SAP calculations are a vital part of building regulation compliance in the UK, and measure the planned energy performance of a new dwelling. Usually updated once every four years, the new SAP 10 won’t be in use until Part L regulations are next updated (likely 2019 or 2020).

However, the documents released by the BEIS and BRE this summer give an essential preview of the changes to come. ll the updates aim to ensure that SAP calculations (and their respective EPCs) more accurately reflect the real-world, as-built performance of a building. Many of the changes affect a building project right from design stage, so we’re keen to get a head start on understanding and planning for them.

Here’s a summary of the top seven most important changes, and what they might mean to you:

Fuel prices and CO2 factors reflect the greening of the grid

Significantly the CO2 emission factor for electricity will be reduced from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh. The current SAP assumes that electricity uses 2.4 times the carbon emissions of a mains gas equivalent – but thanks to the increase of renewable energy technologies in the National Grid, that’s no longer an accurate measurement.

What this means: Lowering the emission factor for electricity will make it much more feasible to incorporate electric heating in a dwelling design, as well as being more true to real-world performance.

Lighting calculations include daylight and newer technologies

Another considerable change that follows SBEM methodologies (the tool used for commercial and public buildings): at the moment, lighting calculations in SAP are very simplistic, only accounting for the number of low-energy light fittings in a dwelling. Now the more accurate calculation will be based on the quantity and efficiency of the fixed lighting in the building, and on the contribution of daylight. The procedure will compare the fixed lighting design with a reference capacity range in SAP, based on the dwelling’s floor area. If the lighting design is outside of this lighting reference range, then additional top-up lighting (using default lighting values) will be automatically added within the software to meet the shortfall.

What this means: A more accurate calculation means recognition of newer and more complex lighting technologies. And it will be important to know more detail about the window and lighting specifications at design stage, so the SAP software doesn’t default to its reference data. Lighting designs will need to perform within the SAP’s lighting reference range to avoid ‘poor’ or ‘surplus’ lighting being added to the calculation in the background.

Thermal bridging recording becomes more exact

This one probably represents the biggest change to existing building design, as the updates move towards a true fabric-first approach. The current SAP allows arbitrary figures to be carbon emissions of a mains gas equivalent – but thanks to the increase of renewable energy technologies in the National Grid, that’s no longer an accurate measurement.

What this means: Lowering the emission factor for electricity will make it much more feasible to incorporate electric heating in a dwelling design, as well as being more true to real-world performance. This will mean psi values will need to be considered alongside U-Values earlier in the design process. The psi values will either need to be pre-calculated by the industry (assuming the details in your construction match the calculation) or bespoke psi values will need to be calculated for each dwelling. Either way, it’ll be essential to get the support of accredited and specialist energy assessment early in the design.

Hot water demand includes showers and baths

At the moment, SAP does not include an assessment of a dwelling’s showers and baths. That changes under SAP 10, which will record the number and type of showers and baths in a dwelling, making for a more precise estimate of actual hot water demand.

What this means: electric instantaneous and mixer showers will need to be individually entered into SAP with their associated flow rates. Flow rate restrictors can be used for mixer showers to a baseline of 6 litres/min, and electric instantaneous showers need to be entered as 9kW or above. This will more than likely increase the dwelling’s energy use in SAP, so should be accounted for at design stage.

Photovoltaic panels change their configuration

Another bid for greater accuracy here: the current SAP allows individual flats to accrue CO2 gains from a PV array installed on the roof of a block of flats, whether or not the array is connected to that flat in particular or just to the landlord’s supply. SAP 10 stops that practice: a PV array connected to the landlord’s supply has no effect on the individual flats in the block; only flats with individual inverters connected to the array can accrue CO2 gains. SAP 10 will also have options to account for battery storage for PV-produced electricity, and gains where a PV array is directly heating an immersion coil in a cylinder, as well as allow the overshading factor used for the PV calculation to be taken from Microgeneration Certification Scheme data.

What this means: current design strategies will need to take these different CO2 reduction targets into account to ensure compliance, and the new options will allow for more flexible, realistic design.

Overheating risk is accounted for

The current SAP does not include any assessment of overheating – an omission that has become more pressing in recent years. SAP 10 seeks to account for as-built circumstances that might affect people keeping their windows open during periods of hot weather.

What this means: if the assessor selects ‘natural ventilation’, there will be a series of questions to answer about the presence of external noise sources and potential security risks. The window opening extent and the air change rates permitted will be affected by these location-based circumstances. This will necessitate a more coordinated consideration of the site location and ventilation strategy risks. The window opening extent and the air change rates permitted will be affected by these location-based circumstances. This will necessitate a more coordinated consideration of the site location and ventilation strategy.

Thermal Mass Parameters (TMPs) reflect real-world conditions

There will no longer be an SAP option to classify a dwelling’s thermal mass parameters (TMPs) as either low, medium or high. Again, these are judged to be too arbitrary to reflect the building’s actual performance.

What this means: SAP 10 will require all assessments to be completed, including a detailed calculation of the building’s actual TMP based on the proposed building materials, constructions, and their kappa values.

We’re keeping informed and prepared for every update as it arrives. To study SAP 10 in more detail, see www.bregroup.com/sap/sap10. Or to talk through how the changes might affect you, give us a call on 01454 317940.

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